What is Secondary Injection Testing?

It is a method of connecting a secondary injection test set to a trip unit (trip device, over current module, protection device, OCR, ETU etc) on a circuit breaker and injecting a simulated current to prove it works at different levels.

Why is it important to Secondary Injection Test Trip Units during a breaker service?

The trip unit on a low voltage breaker (moulded case or air type) is usually an option selected by the system or panel designer to provide protection to the site in the event of a fault or over current occurring.  The trip unit measures the amount of current and calculates its effect on the site system against its settings (usually decided by a commissioning Engineer), and will trip or open the breaker as required.  The larger the current measured, the quicker the breaker should trip or open.

It is an important test to carry out on a trip unit during a service.  By connecting one of our many different manufacturers secondary injection test sets we can ensure that the trip unit, its settings or factory parameters, and associated components are working as they should do.  It is also a key test for a circuit breaker after a mechanical service and inspection, as the breaker is repeatedly charged, closed and opened.  These sequences help ensure key lubrication has worked into the mechanisms that are often found dry and un-serviced.  The test equipment types, and designs, vary greatly but all are designed to prove the breaker protection from very simple to complex methods.  Tests normally carried out, dependant on the specification of trip unit and tester are:

  • Long Time
  • Short Time
  • Instantaneous
  • Ground Fault
  • Earth Leakage


Each of these tests are repeated several times, to ensure reliable, repeatable, operation and trip times. Any inconsistence could imply the trip unit is not working correctly hence not protecting the site systems.

Switchserve are continually assessing customer and site requirements and invest in old and new secondary injection test equipment every year.  We pride ourselves on having a substantial range of key current, and obsolete, manufacturer test equipment that is maintained and calibrated for our use on site and in our workshop.  On occasion where the breaker is obsolete and equipment is not available we use, where possible, our Sverker secondary injection tester to test breaker protection.

What is Primary Injection Testing?

Primary Injection Testing is where an actual current is applied to a breaker to check its protection.  This test is usually done, on low voltage switchgear, in the manufacturers facility only.  This testing can be done on site but requires further heavy test equipment to generate the currents required to test protection; hence the importance and availability of secondary injection testing.  If you require primary injection testing please contact us for further details.

Please contact us for you specific requirements or if you have any questions we can help with.

Switchserve has a vast range of secondary injection test equipment being able to support customers with Air Circuit Breakers and Moulded Case Circuit Breakers from Manufacturers such as:

  • Mitsubishi                                           
    • AE-S
    • AE-SS
    • AE-SW
    • MCCB’s
  • ABB

    • SACE ABB Classic Emax
    • SACE ABB New Emax
  • Merlin Gerin / Schneider
    • Masterpact
    • Masterpact NW
    • NT (compact)
    • MCCB’s
  • Terasaki
    • AT series
    • AR series
  • GE
    • M-Pact
    • M-Pact Classic
    • Entelliguard
  • Siemens/Moeller
    • WL series (awaiting image)
  • Eaton/Cutler Hammer
    • Magnum
    • NRX

and more…